Method for fabricating multilayer environmental barrier coatings

ABSTRACT

A method of making a multilayer environmental barrier coating for a ceramic matrix composite is provided, comprising the steps of: plasma spray coating an oxide-based bond coat over top of the ceramic matrix composite and depositing a columnar top coat over the oxide-based bond coat.

RELATED APPLICATIONS

This application is related to and claims priority to U.S. Provisional Patent Application Ser. No. 61/777,054, filed on Mar. 12, 2013 entitled “Method for Fabricating Multi-Layer Environmental Barrier Coatings.” The subject matter disclosed in that provisional application is hereby expressly incorporated into the present application in its entirety.

TECHNICAL FIELD AND SUMMARY

This present disclosure relates to methods of fabricating multilayer environmental barrier coatings for substrates such as ceramic matrix composites, and in particular, to methods of fabrication that include the combination of plasma spraying and either electron beam physical vapor deposition or directed vapor deposition.

An illustrative embodiment of the present disclosure includes a method of making a multilayer environmental barrier coating for a ceramic matrix composite, comprising the steps of: plasma spray coating an oxide-based bond coat over top of the ceramic matrix composite; selecting a method of applying a columnar top coat over the oxide-based bond coat, wherein the method of applying the columnar top coat is selected from the group consisting of electron beam physical vapor deposition and directed vapor deposition; and depositing a columnar top coat over the oxide-based bond coat according to the selected method of applying the columnar top coat.

In the above and other embodiments, the method of making the multilayer, environmental barrier coating may further include: selecting the method of applying the columnar top coat, being decided by evaluating the benefits and detriments of either the electron beam physical vapor deposition and the directed vapor deposition methods and how those benefits and detriments affect the columnar top coat when sprayed on the oxide-based bond coat; the oxide-based bond coat is selected from the group consisting of mullite, mullite+Si, HfSiO₄+SiO₂+Si, HfSiO₄+SiO₂+Al₂O₃+Si, RE₂Si₂O₇+Al₂O₃+Si, RE₂Si₂O₇+Al₂O₃+SiO₂+Si, HfSiO₄+Al₂O₃+Si, HfSiO₄+Si and SiO₂+Al₂O₃+Si, (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium), the columnar top coat is selected from the group consisting of RE₂Si₂O₇ and RE₂SiO₅ (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium), RE₂O₃-stabilized ZrO₂ (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium), and RE₂O₃-stabilized HfO₂ (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium); the oxide-based bond coat being the mullite+Si wherein the Si is present in an amount between about 10 wt % and about 40 wt %, with the balance being mullite; the oxide-based bond coat being the HfSiO₄+SiO₂+Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO₂ is present in an amount between about 10 wt % and about 30 wt %, and the balance being HfSiO₄; the oxide-based bond coat being the HfSiO₄+SiO₂+Al₂O₃+Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO₂ is present in an amount between about 10 wt % and about 30 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance being HfSiO₄; the oxide-based bond coat being the RE₂Si₂O₇+Al₂O₃+Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance being RE₂Si₂O₇; the oxide-based bond coat being the RE₂Si₂O₇+Al₂O₃+SiO₂+Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO₂ is present in an amount between about 10 wt % and about 30 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance being RE₂Si₂O₇; the oxide-based bond coat being the SiO2+Al₂O₃+Si, wherein the Si present in an amount between about 10 wt % and about 40 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance being SiO₂: the oxide-based bond coat being HfSiO₄+Al₂O₃+Si; wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is HfSiO₄; and the oxide-based bond coat being HfSiO₄+Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, and the balance being HfSiO₄.

Additional features and advantages of these methods will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrated embodiment exemplifying the best mode of carrying out these methods as presently perceived.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure will be described hereafter with reference to the attached drawing which is given as a non-limiting example only, in which:

FIG. 1 is a cross-sectional diagram of a ceramic matrix composite material with an oxide-based bond coat deposited thereon and a columnar top coat deposited on the oxide-based bond coat.

The exemplification set out herein illustrates embodiments of the methods and such exemplification is not to be construed as limiting the scope of the methods in any manner.

DETAILED DESCRIPTION

This present disclosure is directed to methods of fabricating multilayer environmental barrier coatings (EBCs) to suit the characteristics of certain materials such as Silicon-containing ceramics including ceramic Matrix composites (CMCs). Plasma spraying, electron beam physical vapor deposition (EB-PVD), or directed vapor deposition (DVD) are three methods of coating CMCs.

Each deposition method has its own benefits and detriments. One embodiment may use plasma spraying and electron beam physical vapor deposition. Another embodiment may use plasma spraying and directed vapor deposition. By combining layers using these different methods, the benefits of each create distinctive properties to the coatings. For example, an EBC may be formed by combining a plasma sprayed layer which provides the capability to fabricate complex chemistry coatings, with a layer formed by either DVD or EB-PVD which provides the capability to fabricate highly strain-tolerant columnar microstructures and smooth surface finishes. The results are high performance EBCs with a multiple oxide-based bond coat having >2700 F temperature capability and a top coat having −3000 F temperature capability. The following table identifies the benefits and detriments of the various coating processes.

Process Benefits Detriments Plasma Amenability to complex Inability to coat non- Spraying coating chemistries line-of-sight areas Relatively low Rough coating surface manufacturing cost finish Low deposition efficiency Low erosion resistance EB-PVD Smooth coating surface Inability to coat non- (Conventional) finish line-of-sight areas Ability to create highly Difficulty in fabricating strain-tolerant complex coating columnar microstructures chemistries High erosion resistance Low deposition efficiency High manufacturing cost DVD Smooth coating surface Difficulty in fabricating (Enhanced finish complex coating EB-PVD) Ability to create highly chemistries strain-tolerant High manufacturing columnar microstructures cost, but likely Ability to coat non- line- lower than conventional of-sight areas EB-PVD High deposition efficiency High erosion resistance

The benefits of plasma spraying include amenability to complex coating chemistries and relatively low manufacturing cost, while its detriments lode the inability to coat non-line-of-sight areas, rough coating surface finish, low deposition efficiency, and low erosion resistance. In contrast, the benefits of EB-PVD include smooth coating surface finish, ability to create highly strain-tolerant columnar microstructures and high erosion resistance. Its detriments include an inability to coat non-line-of-sight areas, difficulty in fabricating complex coating chemistries, low deposition efficiency and high manufacturing cost. The DVD (or enhanced EB-PVD) has non-line-of-sight coating capabilities and improved deposition efficiency as compared to conventional EB-PVD.

Again, the fabrication method for each coating layer is selected by considering the benefits and detriments of each process in conjunction with the complexity of the chemistry and the function of each layer. EB-PVD or DVD may be used for the top coat of airfoils because of their smooth surface finish for aerodynamic performance and better erosion resistance as compared to plasma spraying. EB-PVD or DVD may also be used for layers with high coefficient of thermal expansion (CTE) mismatch with CMC. Layers having high CTE mismatch with CMC may cause high residual stresses and therefore experience short thermal cycling life. CTE mismatch stresses can be significantly mitigated by creating a highly strain tolerant columnar microstructure using the EB-PVD or DVD processes. Plasma spraying may be used for layers with a complex chemistry. Multiple phases react at high temperatures to form glass-containing reaction products that create strong chemical bonding for long steam cycling life.

An illustrative embodiment provides a combination of a plasma-sprayed, complex oxide-based bond coat and either an EB-PVD or DVD-based rare earth silicate, stabilized zirconia or stabilized hafnia top coat. This combination provides the EBCs with a high temperature bond coat with a temperature capability exceeding the temperature capability of current Silicon (Si) bond coats (−2460 F), along with a highly strain-tolerant and water-vapor-resistant, low thermal conductivity top coat. The high temperature bond coat enables the implementation of high temperature CMCs (2700 F CMC) in gas turbines, while the highly strain-tolerant and water-vapor-resistant, low thermal conductivity top coat increases the EBC surface temperature capability to about −3000 F.

Examples of plasma sprayed layers include oxide-based high temperature bond coats with complex chemistry, such as mullite (3Al₂O₃-2SiO₂), mullite+Si, HfSiO₄+SiO₂+Si, HfSiO₄+Al₂O₃+SiO₂+Si, RE₂Si₂O₇+Al₂O₃+Si, RE₂Si₂O₇+Al₂O₃+SiO2+Si, HfSiO₄+Al₂O₃+Si, HfSiO₄+Si and SiO₂+Al₂O₃+Si, (where RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium). When the oxide-based bond coat is mullite+Si—the Si is present in an amount between about 10 wt % and about 40 wt % and the balance is mullite. When the oxide-based bond coat is HfSiO₄+SiO₂+Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO₂ is present in an amount between about 10 wt % and about 30 wt %, and the balance is HfSiO₄. When the oxide-based bond coat is HfSiO₄+SiO₂+Al₂O₃+Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO₂ is present in an amount between about 10 wt % and about 30 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is HfSiO₄. When the oxide-based bond coat is RE₂Si₂O₇+Al₂O₃+Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is RE₂Si₂O₇. When the oxide-based bond coat is RE₂Si₂O₇+Al₂O₃+SiO2+Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO₂ is present in an amount between about 10 wt % and about 30 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is RE₂Si₂O₇. When the oxide-based bond coat is HfSiO₄+Al₂O₃+Si;—the Si is present in an amount between about 10 wt % and about 40 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is HfSiO₄. When the oxide-based bond coat being HfSiO₄+Si—the Si is present in an amount between about 10 wt % and about 40 wt %, and the balance is HfSiO₄. Lastly, when the oxide-based bond coat is SiO2+Al₂O₃+Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the Al₂O₃ is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is SiO₂.

Examples of EB-PVD or DVD layers include ESC top coats of are earth silicate (RE₂Si₂O₇ and RE₂SiO₅), RE₂O₃-stabilized ZrO₂ and RE₂O₃-stabilized HfO₂ (where RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium). Rare earth monosilicate (RE₂SiO₅), RE₂O₃-stabilized ZrO₂ and RE₂O₃-stabilized HfO₂, have CTEs substantially higher than CMC and therefore are desirable to be fabricated in low modulus, strain tolerant columnar microstructure to mitigate CTE mismatch stresses.

The substrate may include any of the following: a Si-containing ceramic, such as silicon carbide (SiC), silicon nitride (Si₃N₄), a CMC having a SiC or Si₃N₄ matrix, silicon oxynitride, and silicon aluminum oxynitride; a Si-containing metal alloy, such as molybdenum-silicon alloys (e.g. MoSi₂) and niobium-silicon alloys (e.g. NbSi₂); and an oxide-oxide CMC. CMCs comprise a matrix reinforced with ceramic fibers, whiskers, platelets, and chopped or continuous fibers.

A cross-sectional diagram of a ceramic matrix composite material with an oxide-based bond coat deposited thereon, and a columnar top coat deposited on the oxide-based bond coat is shown in FIG. 1. An illustrative example of an EBC that combines plasma sprayed, high temperature oxide-based bond coat 4 and either a DVD or EB-PVD processed, highly strain-tolerant columnar top coat 6, on a CMC or other Si-containing ceramic 8. The choice of whether columnar top coat 6 is formed from either DVD or EB-PVD is determined by the particular benefits one or the other imparts, as shown in the table above.

Although the present disclosure has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present disclosure and various changes and modifications may be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as set forth in the following claims. 

What is claimed is:
 1. A method of making a multilayer environmental barrier coating for a ceramic matrix composite, the method comprising: plasma spray coating an oxide-based bond coat over top of the ceramic matrix composite, wherein the oxide-based bond coat consists of HfSiO₄+SiO₂+Al₂O₃+Si, and wherein the Si is present in the oxide-based bond coat in an amount between about 10 wt. % and about 40 wt. %, the SiO₂ is present in the oxide-based bond coat in an amount between about 10 wt. % and about 30 wt. %, the Al₂O₃ is present in the oxide-based bond coat in an amount between about 0.1 wt. % and about 10 wt. %, and the balance of the oxide-based bond coat is HfSiO₄; selecting a method of applying a columnar top coat over the oxide-based bond coat, wherein the method of applying the columnar top coat is selected from the group consisting of electron beam physical vapor deposition and directed vapor deposition; and depositing a columnar top coat over the oxide-based bond coat according to the selected method of applying the columnar top coat.
 2. The method of making the multilayer environmental barrier coating of claim 1, wherein selecting the method of applying the columnar top coat is decided by evaluating benefits and detriments of either the electron beam physical vapor deposition and the directed vapor deposition methods and how those benefits and detriments affect the columnar top coat when sprayed on the oxide-based bond coat.
 3. The method of making the multilayer environmental barrier coating of claim 1, wherein the columnar top coat is selected from the group consisting of RE₂Si₂O₇ and RE₂SiO₅ (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium), RE₂O₃-stabilized ZrO₂ (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium), and RE₂O₃-stabilized HfO₂ (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium).
 4. A method of making a multilayer environmental barrier coating for a ceramic matrix composite, the method comprising: plasma spray coating an oxide-based bond coat over top of the ceramic matrix composite, wherein the oxide-based bond coat consists of HfSiO₄+Al₂O₃+Si, and wherein the Si is present in the oxide-based bond coat in an amount between about 10 wt. % and about 40 wt. %, the Al₂O₃ is present in the oxide-based bond coat in an amount between about 0.1 wt. % and about 10 wt. %, and the balance of the oxide-based bond coat is HfSiO₄; selecting a method of applying a columnar top coat over the oxide-based bond coat, wherein the method of applying the columnar top coat is selected from the group consisting of electron beam physical vapor deposition and directed vapor deposition; and depositing a columnar top coat over the oxide-based bond coat according to the selected method of applying the columnar top coat.
 5. A method of making a multilayer environmental barrier coating for a ceramic matrix composite, the method comprising: plasma spray coating an oxide-based bond coat over top of the ceramic matrix composite, wherein the oxide-based bond coat consists of HfSiO₄+Si; and wherein the Si is present in the oxide-based bond coat in an amount between about 10 wt. % and about 40 wt. %, and the balance of the oxide-based bond coat is HfSiO₄; selecting a method of applying a columnar top coat over the oxide-based bond coat, wherein the method of applying the columnar top coat is selected from the group consisting of electron beam physical vapor deposition and directed vapor deposition; and depositing a columnar top coat over the oxide-based bond coat according to the selected method of applying the columnar top coat. 